1. Field of the Invention
This application relates to a system and method for producing steam from a contaminated water feed for Enhanced Oil Recovery (EOR). This invention relates to processes for directly using steam energy, preferably superheated dry steam, for generating additional steam from contaminated water by direct contact, and using this produced steam for various uses in the oil industry, and in other industries as well. The produced steam can be injected underground for Enhanced Oil Recovery. It can also be used to generate hot process water for the mining oilsands industry. The high pressure drive steam is generated using a commercially available, non-direct steam boiler, co-gen, Once Through Steam Generator (OTSG) or any steam generation system or steam heater. Contaminates, like suspended or dissolved solids within the low quality water feed, can be removed in a stable solid (former Liquid Discharge) system. The system can be integrated with a combustion gas fired Direct Contact Steam Generator (DCSG) for consuming liquid waste streams or with distillation water treatment systems.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The injection of steam into heavy oil formations has proven to be an effective method for EOR and it is the only method currently used commercially for recovery of bitumen from deep underground oilsands formations in Canada. It is known that EOR can be achieved when combustion gases, mainly CO2, are injected into the formation, possibly with the use of a DCSG as described in my previous applications. The problem is that oil producers are reluctant to implement significant changes to their facilities, especially if they include changing the composition of the injected gas to the underground formation and the risk of corrosion in the carbon steel pipes due to the presence of the CO2. Another option to address these concerns and generate steam from low grade produced water with Zero Liquid Discharge (ZLD) is to operate the DCSG with steam instead of a combustion gas mixture that includes, in addition to steam, other gases like nitrogen, carbon dioxide, carbon monoxide, etc. The driving steam is generated by a commercially available non-direct steam generation facility. The driving steam is directly used to transfer liquid water into steam and solid waste. In EOR facilities, most of the water required for steam generation is recovered from the produced bitumen-water emulsion. The produced water has to be extensively treated to remove the oil remains that can damage the boilers. This process is expensive and consumes chemicals. The Steam Drive-Direct Contact Steam Generator (SD-DCSG) can consume the contaminated water feed for generating steam. The SD-DCSG can be a standalone system or can be integrated with a combustion gas DCSG, as described in this application. The proposed SD-DCSG is also suitable for oilsands mining projects where the Fine Tailings (FT) or Mature Fine Tailings (MFT) are heated and converted to solids and steam using the driving steam energy. The produced steam from the SD-DCSG can be used to heat the process water in a direct or non-direct heat exchange. The hot process water is mixed with the mined oilsands ore during the extraction process.
The method, as described, includes generating additional steam from highly contaminated oily water with an option for zero liquid waste discharge. Superheated steam from an industrial boiler is used as the driving force for generating additional steam in a direct contact heat transfer with the contaminated water. Fine Tailings from tailing ponds can be also used. A “tailor made” pressure and temperature steam, as required for injection into the underground oil bearing formation, is generated. This process allows for generation of additional lower temperature steam from waste water in a high efficiency energy process. The amount of additional steam generated increases with the temperature of the driving steam, and with the reduction of the pressure of the formation. For low pressure shallow formations, more steam can be produced in comparison to deep, high pressure formations. Another option is to recycle a portion of the produced steam through a heater and use it as the driving steam, and thereby minimizing the need for external steam as a heat energy source. A portion of the oil component in the water feed will be converted into hydrocarbon gas, basically serving as a solvent. Additional solvents can be added and injected with the steam to improve the oil recovery. The presented technology has a high thermal efficiency capable of consuming contaminated hot produced water, without the need to reduce the heat to allow effective water treatment. The process can convert the existence of oil contaminates within the feed water into an advantage by generating solvent. This steam generation direct contact facility can be located in close proximity to the SAGD pads to use the hot produced water and inject the produced steam into the injection wells.
The steam for the SD-DCSG can be provided directly from a power station. The most suitable steam will be medium pressure, super-heated steam as is typically fed to the second or third stage of steam turbine. A cost efficient, hence effective system will be used to employ a high pressure steam turbine to generate electricity. The discharge steam from the turbine, at a lower pressure, can be recycled back to the boiler re-heater to generate a superheated steam which is effective as a driving steam. Due to the fact that the first stage turbine, which is the smallest size turbine, produces most of the power (due to a higher pressure), the cost per Megawatt of the steam turbine will be relatively low. The efficiency of the system will not be affected as the superheated steam will be used to drive the SD-DCSG directly and to generate injection steam for an enhanced oil recovery unit with Zero Liquid Discharge (ZLD). A ZLD facility is more environmentally friendly compared to a system that generates reject water and sludge.
The definition of “Steam Drive-Direct Contact Steam Generation” (SD-DCSG) is that steam is used to generate additional steam from a direct contact heat transfer between the liquid water and the combustion gas. This is accomplished through the direct mixing of the two flows (the water and the steam gases). In the SD-DCSG, the driving steam pressure is similar to the combustion pressure and the produced steam is a mixture of the two.
The driving steam is generated in a Non-Direct Steam Generator (like a steam boiler with a steam drum and a mud drum) or in a “Once Through Steam Generator” (OTSG) COGEN that uses the heat from a gas turbine to generate steam, or in any other available design. The heat transfer and combustion gases are not mixed and the heat transfer is done through a wall (typically a metal wall), where the pressure of the generated steam is higher than the pressure of the combustion. This allows for the use of atmospheric combustion pressure. The product is pure steam (or a steam and water mixture, as in the case of the OTSG) without combustion gases.
The excessive energy in the superheated steam is used for generating additional lower temperature steam for injection into the formation. The use of evaporation water treatment facilities in the oilsands industry allows for the production of superheated steam. The proposed method uses Direct Contact Steam Generation where the superheated steam gas is in direct contact with the liquid produced water. Hydrocarbons, like solvents, within the produced water will be directly converted to gas and recycled back to the formation, possibly with additional solvents that can be added to the steam flow. The method generates a “tailor made” pressure and temperature steam, as required for injection into the underground oil bearing formation while maximizing the amount of the generated steam. The simulation in this application shows that for a 263 psi system with a constant feed of 25° C. water flow at 1000 kg/hour, there is a need for 12.9 tons/hour of 300° C. steam to gasify 1 ton/hour of liquid water. When higher temperature (500° C.) driving steam is used, there is a need for only 4.1 tons/hour of steam. The example simulation results show that the amount of produced steam increases by 314% with an increase in the driving steam temperature. The pressure impact simulation was based on driving steam being at a constant temperature of 450° C. and with one ton/hour of 25° C. water feed. The simulation shows that at pressure of 263 psi, 4.9 tons/hour of driving steam is used to gasify the water feed. At a higher pressure of 1450 psi, 5.1 tons/hour driving steam will be used. The results show that a pressure increase slightly reduces the amount of produced steam. The impact of the feed water temperature on the system performance was also simulated. It was shown that for a system of constant 12 kw heat source at 600 psi, 15.1 kg/hour of feed water was gasified to generate injection steam. When the produced water temperature was 220° C., 22.4 kg/hour was gasified. This shows that the produced water temperature has a large impact on the overall performance and that by using the high temperature produced water, the system performance can be increased by close to 150%. The simulation shows that hydrocarbons, like solvents with the produced water, will be converted to gas and injected with the steam. The system can also include a heater to recycle a portion of the produced steam as the driving steam that will be produced locally. There was also shown to be an advantage to using hot produced water and minimizing the produced steam pressure drop. This can be achieved by locating the system close to the injection and production well pad. Make-up steam supplied from a remote steam generation facility can be used to operate a steam ejector with a local steam heater, or be used as the superheated driving steam. The system is ZLD in nature. It can also produce liquid waste if liquid disposal is preferred.
There are patents and disclosures issued in the field of the present invention. U.S. Pat. No. 6,536,523, issued to Kresnyak et al. on Mar. 25, 2003, describes the use of blow-down heat as the heat source for water distillation of de-oiled produced water in a single stage MVC water distillation unit. The concentrated blow-down from the distillation unit can be treated in a crystallizer to generate solid waste.
U.S. patent application Ser. No. 12/702,004, filed by Minnich et al. and published on Aug. 12, 2010, describes a heat exchanger that operates on steam for generating steam in an indirect way from low quality produced water that contains impurities. In this disclosure, steam is used indirectly to heat the produced water that includes contaminates. By using steam as the heat transfer medium, the direct exposure of the low quality water heat exchanger to fire and radiation is prevented, thus there will be no damage due to the redaction of the heat transfer. The concentrated brine is collected and delivered for disposal or to a multi stage evaporator to recover most of the water and there generates a ZLD system. The heat transfer surfaces between the steam and the produced water will have to be clean or the produced water will have to be treated. The concentrated brine, possibly with organics, will be treated in a low pressure, low temperature evaporator to increase the concentration; the higher the concentration is, the lower the temperature. In my application, due to the direct approach of the heat transfer, the system in ZLD with the highest concentration, possibly up to 100% liquid recovery, while generating solid waste, is at the first stage at a higher temperature due to the direct mixture with the superheated dry steam that converts the liquid into gas and solids.
U.S. Pat. No. 7,591,309, issued to Minnich et al. on Sep. 22, 2009, describes the use of steam for operating a pressurized evaporation facility where the pressurized vapor steam is injected into underground formations for EOR. The steam heats the brine water which is boiled to generate additional steam. To prevent the generation of solids in the pressurized evaporator, the internal surfaces are kept wet by liquid water and the water is pre-treated to prevent solid build up. The concentrated brine is discharged for disposal or for further treatment in a separate facility to achieve a ZLD system. To achieve ZLD, the brine evaporates in a series of low pressure evaporators (Multi Effect Evaporator).
U.S. Pat. No. 6,733,636, issued to Heins on May 11, 2004, describes a produced water treatment process with a vertical MVC evaporator.
U.S. Pat. No. 7,578,354, issued to Minnich et al. on Aug. 25, 2009, describes the use of Multi Effect Distillation (MED) for generating steam for injection into an underground formation.
U.S. Pat. No. 7,591,311, issued to Minnich et al. on Sep. 22, 2009, describes a process of evaporating water to produce distilled water and brine discharge, feeding the distilled water to a boiler, and injecting the boiler blow-down water from the boiler into the produced steam. The solids and possibly volatile organic remains are carried with the steam to the underground oil formation. The concentrated brine is discharged in liquid form.
U.S. Pat. No. 4,398,603, issued to Rodwell on Aug. 16, 1983, describes producing steam from a low quality feed water. Superheated steam is introduced into liquid water in a vessel. The mixture is done in a liquid environment where minerals (solids) are participates and are removed in a liquid phase from the vessel by withdrawing a waste water stream. Due to the excess heat within the superheated steam, a portion of the liquid feed water evaporates and produces saturated steam. Because all mixing with the steam is done in a liquid environment, the process can only produce saturate (wet) steam with waste liquid discharge for removing the solids.
This invention's method and system for producing steam for extraction of heavy bitumen includes the steps as described in the patent figures.
The advantage and objective of the present invention are described in the patent application and in the attached figures.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.